Traps with ions of Paul and Penning

The traps with ions are devices making it possible to store particle S charged during one long life, in particular with an aim of measuring their properties with precision.

The traps of Paul and Penning in common have the use of a Electric field quadripolar, high frequency (about some MHz) in the trap of Paul , and constant in the trap of Penning , where it is combined with an intense magnetic field (about 5 Teslas). The placement of the traps with ions in the field of the atomic Spectroscopie of precision was worth with Hans Dehmelt (with the trap of Penning) and with Wolfgang Paul (with the trap bearing its name) the Nobel Prize of physics in 1989, divided with Norman Foster Ramsey for its work on the atomic clocks.

One will limit oneself here to the description of the trap of Penning.

Principle of the trap of Penning

The trap of Penning , also called cell ICR ( cell with ionic cyclotronic resonance ), is a device making it possible to store particle S charged, thanks to the combination of a uniform Magnetic field and a constant Electric field quadripolar. This device is particularly well adapted to the precise measurement of the properties of the Ion S and the subatomic particles stable having an electric charge. It is the Dutch physicist F.M. Penning who had of it the original idea in 1936, but the merit of its implementation concrete is allocated to the American physicist Hans Dehmelt.

The traps of Penning use an axial homogeneous magnetic field to confine the particles in the median plane, and a quadripolar electric field to confine them according to the axis of symmetry of the trap. The magnetic field forces the particles charged to move according to spirals, and the electric field prevents that the particles do not leave the trap when they follow the lines of magnetic field.

The device of generation of the electric field consists of two groups of electrodes in hyperboloidal form of of revolution: on the one hand a ring, and on the other hand two axial cups. A constant Potential difference is applied between the ring and the cups, these last being subjected to a repulsive potential for the particles to store (potential positive to store positive ions), and the ring being subjected to a potential of contrary sign. The electric field thus created produces a collar in the center of the trap, which makes it possible to carry out containment in the axial direction.

The generation of the magnetic field is carried out by a toroidal electromagnet , preferably superconductive. The field created is applied according to the axis, which obliges the particles charged to traverse circular orbits, thus maintaining inside the trap.

The particles thus trapped undergo three types of oscillations:

an axial oscillation
Two oscillations in the radial plan, similar to those of a Spinning top moving on the ground:

an oscillation magnetron corresponding to the circular orbit of the particle within the trap,
an oscillation cyclotron corresponding to the rotation of the particle “on itself”.

The frequency of the oscillation cyclotron depends on the report/ratio of the electric Charge with the Masse, and of the intensity of the Magnetic field. Its measurement being able to be carried out with a high degree of accuracy, one can deduce very precisely the mass from it from the trapped particle or ion.

The use of the trap of Penning has two advantages compared to the trap to radio frequencies of Paul. First advantage, only of the static fields are used in the trap of Penning, which avoids microphone-displacements related to dynamic fields, as production of heat which results from it. Second advantage, the trap of Penning can be increased without decreasing its effectiveness. It is then possible to maintain the ion trapped at a longer distance from the surface of the electrodes, which reduces the harmful phenomena of heating and quantum Décohérence.

On the other hand, the trap of Penning presents compared to the trap of Paul the disadvantage of not being able to store particles of positive and negative loads simultaneously.

Applications

The traps of Penning are usually used with CERN to store Antiproton S.

Systems of propulsion containing Antimatière intended for the space flight could use a process of this type for the fuel storage.

Their principal application is however the measurement of precision. For example, the most precise measurements of the masses of many particles (electron, Proton) or atoms (² H, ¹² C, ²⁰ , ²⁸ If) were carried out by using traps of Penning.

The particles stored in a trap of Penning can be cooled by various methods, like the cooling by laser.

Another recent application relates to the realization of quantum computers and the quantum treatment of information.

See too

Internal bonds

quantum Spectrometry mass
Physical of plasmas
Mechanical

External bonds

Nobel Prize in Physics 1989
Theory and Simulation off Penning Traps
Ion-Trap Quantum Computation
The High-precision Penning Trap Farmhouse Spectrometer SMILETRAP in Stockholm, Sweden
Spectrometry mass with transform of Fourier: basic concepts and some applications
Notes of course of Claude Cohen-Tannoudji to the Collège de France (school year 1984-1985): (or course of all the year )

Electron in a trap of Penning. Eigen frequencies and energy levels (January 29th)
Electron in a trap of Penning. Process of relieving (February 5th)
Electron in a trap of Penning. Excitation and detection of various resonances (February 12th)
Electron in a trap of Penning. Excitation and detection of various resonances (continuation and end) (February 26th)

Random links: